1. Field of the Invention
The present invention relates generally to the fields of synthetic filaments and fabrics made therefrom. More particularly, it concerns synthetic filaments that have both low surface energy and high strength.
2. Description of Related Art
Fabrics which are water-repellent (i.e. provide a barrier to moisture) while allowing the passage of water vapor and other gases are desirable for use in apparel, shoes, tents and camping equipment, packaging, medical apparel, and medical supplies. Such fabrics require fibers that have both a low surface energy to repel water and a strength high enough to be processible into a useful fabric. Other desirable fabrics are both water-repellent and do not allow the passage of water vapor and other gases, for use in airtight packaging and medical supplies.
In packaging, protective apparel, and industrial filtration, a need exists for fabrics that are stable to both heat and chemicals. Such fabrics require fibers both low in surface energy and high enough in strength to be processible into a useful fabric, as well as heat and chemical resistance.
One class of water-repellent fabrics are those made by applying a finish to a fabric or its component filaments before or after the weaving or knitting process. The finish is intended to provide the low surface energy needed to repel water. However, such finishes tend to have poor durability and washfastness.
A second class of water-repellent fabrics are those comprising water-repellent materials. An example of this class is a fabric comprising polytetrafluoroethylene (PTFE) sold by W. L. Gore Inc. under the trade name GORE-TEX.RTM.. Known uses of PTFE fabrics are limited to lamination of the PTFE fabric to a textile fabric. This suggests that PTFE fabrics, although having low surface energy, do not have high enough strength to be useful fabrics per se.
Therefore, it is desirable to have a textile fabric made of filaments that exhibit low surface energy and strength high enough to be processible into useful fabrics. It is also desirable for such filaments to be produced by high throughput, economical spinning technology. Although filaments with a core/sheath structure wherein the sheath comprises a halogenated polymer are known (Chimura et al., U.S. Pat. Nos. 3,930,103 and 3,993,834), the core of the known filaments comprises primarily methyl methacrylate, and is not useful in forming moisture-resistant fabrics. Although core/sheath filaments wherein the core comprises nylon and the sheath comprises a grafted olefinic polymer are known, such as Tabor et al., U.S. Pat. No. 5,372,885, no such filaments are known to comprise a sheath useful in heat- and chemical-resistant fabrics.